The Lync Server Front-End service terminated with the following service-specific error: A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file.

2. Event 7031 Service Control Manager

The Lync Server Front-End service terminated unexpectedly. It has done this 1 time(s). The following corrective action will be taken in 180000 milliseconds: Restart the service.